1. Field of the Invention
The present invention relates to pneumatic power tools and more particularly to a two speed gear system for power drills capable for use both in drilling and countersinking operations.
2. Description of the Related Art
In aircraft assembly thousands of rivets are installed to hold the skin to the substructure of the aircraft. Surface finishes in the holes and the countersink surfaces for these rivets are critically important and are closely inspected. Experience has shown that tool speed and torque affect the surface tolerances.
Often one tool is used for the relatively high speed drilling of holes and a second tool is used for the relatively low speed high torque countersinking of the drilled holes.
In the aircraft industry, pneumatic-tools, driven by air motors powered by compressed air are often used. The air motors are physically small and light for the high torque and power that it delivers. The air motor starts almost instantly and is inherently safe as compared to electric motors.
In a majority of pneumatic tools spring-loaded torque clutches are used. Units are available in which the driving bit is stopped by the stall torque principle, the magnitude of the torque that stalls the motor being governed by the air pressure setting.
Two systems of torque control are available for pneumatic tools. The first is the minimum torque indication system where the normal stalled torque motors are used in a conventional manner, but with a visual indication to the operator that the minimum torque value required has been achieved.
The second is a torque controlled motor system with visual indication. This system employs standard motors, each fitted with a control top. The torque reaction through the motor body is used to initiate an air signal which passes to the control top and shuts off the air to the motor. The movement of the control top shuttle valve actuates a relay which switches on an indicator light.
There is a need for a single pneumatic tool which is capable of both drilling and countersinking holes. Such pneumatic device must be capable of drilling the holes at high speed and then countersinking the holes at relatively low speed, but high torque.
The present invention provides a single power tool having one speed for drilling and another for countersinking with increased torque for countersinking by incorporating two planetary gear systems. The first planetary system transmits power to the drill. Upon completion of the hole drilling cycle, the second planetary system is cammed into mesh, resulting in a more desirable, reduced working speed and increased torque to perform the countersinking operation.